Clarification on WATERGEM - Reg

Question

Sir, 
 I developed a model using WATERGEM for the pumping water from Reservoir (Sump) to 11 Elevated tanks located in the Habitations. The analysis report shows reverse flow from some of elevated tanks against pumping. 
 Can WATERGEM be used for analyzing pumping main to feed water to elevated Tanks or only for distribution network. 
 Expecting your able support Early. 
 Regards, 
 Dr.K.Ravichandran,M.E.,Ph.D.,

Yashodhan Joshi · Answer

Heelo Dr. Ravichandran, 
 Yes, you can use WaterGEMS to design and analyze pumping stations supplying to ESR's. As far as the reverse flow is concerned, check your pump head and discharge values and confirm if the pump orientation and downstream pipe are both flowing "towards" the elevated tanks. Also check the orientation of the connecting pipe. Ensure that the start node is the "pump" and stop node is the "tank". See the below article for more details on this; 
 Why do I sometimes see a negative flow through a pipe? 
 Let me know if this helps. 
 If this does not answer your query, please share some screenshots (maybe showing the reverse flow) to understand.

Yashodhan Joshi · Answer

Hello Dr. Ravichandran, 
 I checked your model and following are my observations; 
 1. You have assigned demands at all nodes in decreasing order from the source to your branches. E.g. Junction J-2 and J-3 have a demand of 434 l/min but the downstream J-6 and J-7 have a demand of 418 l/min. If your objective is to supply only to the ESR's then why are there demands at intermediate junctions? You don't need to add demands at intermediate junctions like this. 
 For example in your model you want a flow of (434 - 418 = 16 l/min) in pipe P-5, then you have to only add the demand as 16 l/min at the downstream junction i.e. J-6. 
 In WaterGEMS demand has to be added at the network endpoints. From your source to your destination you only have to specify the required demand at the destination. Your destination maybe a simple junction, then add only the required demand at that junction. If you only wish to model the connections till the ESR's you can add the demands at the tanks. These demands could be the estimated flow supplied from these ESR's. If these ESR's supply to some habitation, calculate the total demand required by that habitation and assign it to the tank. This is if you wish to model the network till the ESR level only. 
 2. I also saw that you are performing Steady State Analysis while running, In steady state analysis the hydraulic grade of the tank is taken as constant which is the "Elevation (minimum)". Since it is still higher than the pump suction level the flow is occurring in the reverse direction. For this condition you can use Extended Period Simulation so that you can see that the pump is discharging from time = 1. See the below article for more details on this; 
 Run an Extended Period Simulation (EPS) 
 3. Another suggestion is the use of Flow Control Valves (FCV's) to control the inflow to these ESR's and prevent back flow. Using FCV's you can control the flow entering the tank to allow for controlled filling while maintaining an equilibrium with the system. 
 Hope this helps.